Method for mounting parts

ABSTRACT

A method for mounting parts may include recognizing a particular part feeder where a part to be mounted is contained among a plurality of part feeders, moving a head unit to a position for picking up a part on the part feeder, moving an image sensor installed to be capable of moving to a position close to the particular part feeder, picking up a part from the particular part feeder with a suction nozzle installed at the had unit, moving the head unit to a position above the image sensor, detecting an image of the part held by the suction nozzle, moving the suction nozzle to a printed circuit board from the image sensor, and aligning the part with the printed circuit board while determining and compensating for an error generated when the part is picked up, and mounting the aligned part on the printed circuit board.

This is a division of Application No. 09/617,125, filed Jul. 14, 2000,now U.S. Pat. No. 6,634,091 which is currently pending and isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a part mounter and a method formounting parts, and more particularly, to a part mounter and a methodfor mounting parts by which the required time and the distance equipmentmust move for mounting parts is minimized and the position of the partsis precisely recognized.

2. Description of the Related Art

In general, electronic parts such as semiconductor packages are mountedon a printed circuit board by using a part mounter. The part mounterpicks up electronic parts supplied by a part supply portion such as atray feeder or a tape feeder using vacuum suction and mounts theelectronic parts at predetermined positions on the printed circuitboard. Here, a head unit moves the electronic part to an image sensor toobtain information on the posture of the part held by a suction isnozzle. As the image sensor, a vision camera (a line CCD or an area CCD)is used. The image sensor detects state of the part held by the partsuction portion so that information on the posture of the part isobtained. The part suction portion corrects the posture of the held partaccording to the image information and then mounts the part on theprinted circuit board.

FIG. 1 is a perspective view showing the structure of a typical partmounter. Referring to the drawing, the part mounter includes a firstY-axis 12 and a second Y-axis 13, an X-axis 11 moving along the firstand second Y-axes 12 and 13, and a head unit 14 installed to be capableof moving along the X-axis 11. A suction nozzle 15 is installed at thehead unit 14 to be capable of rotating and moving up and down. A printedcircuit board (PCB) 25 is transferred by a conveyer 19 to the positionof a part 20 to be mounted. The head unit 14 moves between part feeders18 a, 18 b, 18 c, 18 d and 18 e, and the PCB 25. The suction nozzle 15moves up and down and/or rotates to hold a part and mounts it on the PCB25. At least one among the part feeders 18 a, 18 b, 18 c, 18 d and 18 emay be a tape feeder or a tray. During a mounting process, the head unit14 passes above an image sensor 16. The image sensor 16 is fixed at oneside of the part mounter and detects the part held by the suction nozzle15 so that it corrects a positional error generated when a part is heldby the suction nozzle 15. The image sensor 16, for example, may have animage detecting device such as a vision camera (a line CCD or an areaCCD).

FIG. 2 is a view schematically showing the path along which the headunit 14 shown in FIG. 1 moves. Referring to the drawing, the suctionnozzle 15 of the head unit 14 picks up a part from the part feeders 18a, 18 b, 18 c, 18 d and 18 e and then moves to the position directlyabove the image sensor 16. The image sensor 16 senses the part held bythe suction nozzle 15. Through a detecting process performed by theimage sensor 16, an error generated when the part is held by the suctionnozzle 15 can be recognized. Next, the head unit moves above a mountingposition P on the PCB 25. The suction nozzle 15 of the head unit 14descends and mounts the part at the mounting position P of the PCB 25.Here, to correct an error recognized through the sensing process, thehead unit 14 changes its position in the coordinate system or thesuction nozzle 15 rotates and then the part is mounted.

In the part mounter having the above structure, since the head unit 14must travel from the part feeders 18 a, 18 b, 18 c, 18 d and 18 e to thepart mounting position P on the PCB 25 through the image sensor 16, thepath of movement is long and complicated. That is, since the imagesensor 16 is fixed at a particular position, the head unit 14 must moveto the position directly above the image sensor 16 so as to sense thestate of the held part.

FIG. 3 is a view showing an image of a state in which a part is held bythe suction nozzle 15, which is taken by an image sensing apparatus.Referring to the drawing, the center of the suction nozzle 15 matchesthe central point A of an image 121. That is, when the suction nozzle 15picks up a part 111 and moves just above the image sensor 16, the centerof the suction nozzle 15 is designed to match the center of the imagesensor 16. Thus, when a sensing process is performed by the image sensor16, the center point A of the image 121 substantially matches the centerof the suction nozzle 15. This is because a typical image recognitionapparatus is fixed at one side of a part supply portion of a partmounter and the head unit 14 moves to a particular position after movingalong a set path, that is, the center of the suction nozzle 15 matchesthe center of the image 121.

When the image sensing is performed after the suction nozzle 15 haspicked up a part, the positional information of the central point O of apart is recognized with information on the size and shape of the part.Next, information on the tilt of the part is recognized by theinformation on the shape of the part. As shown in FIG. 3, recognizingthe distance separated in the X direction and Y direction between thecentral point A of the image 121 and the central point O of the part111, and a rotational degree θ is recognized and the separated distanceand the rotational degree are compensated for.

However, to correct the error generated when the part is held, the imagesensor 16 must be maintained in a fixed state. This is because thecentral point of the suction nozzle 14 must match the central point A ofthe monitor 121 to recognize the error when suctioning the part. Thus,if the central point of the suction nozzle 14 does not match the centralpoint of the image 121 during the sensing process, performing correctionan error is not possible. The positional information with respect to thenozzle is indirectly obtained and it is assumed that the abovepreconditions are met. Also, at least one of the image sensor 16 and thehead unit 14 must be fixed.

SUMMARY OF THE INVENTION

To solve the above problems, it is an object of the present invention toprovide a part mounter and a method for mounting parts so that partmounting work is performed quickly while correcting an error generated.

Accordingly, to achieve the above objects, there is provided a partmounter comprising a plurality of part feeders for storing and supplyinga plurality of parts, a conveyer for transferring a printed circuitboard, a head unit capable of moving and having a suction nozzle forpicking up a part from the part feeders and mounting the part on theprinted circuit board on the conveyer, and an image sensor installed tomove along a path crossing a movement path of the head unit, fordetecting an image of the part held by the suction nozzle.

It is preferred in the present invention that at least one referenceportion, which is detected if not covered by the part when the imagesensor detects an image of the part held by the suction nozzle, isprovided at the head unit.

Also, it is preferred in the present invention that the image sensormoves close to the part feeder where a part is picked up.

Also, it is preferred in the present invention that the image sensormoves to a position where a path along which the head unit moves,between a position where a part is picked up from the part feeder and aposition where the part is mounted on the printed circuit board, and apath along which the image sensor moves cross.

Also, it is preferred in the present invention that the image sensor ismoved by a motor for providing a driving force, a ball screw rotated bythe motor, and a bushing and a linear guide member installed at one sideof the image sensor and coupled to the ball screw.

Also, it is preferred in the present invention that the image sensor iscapable of moving by a linear motor.

Also, it is preferred in the present invention that the head unit isinstalled to be capable of moving along an X-axis which is installed tobe capable of moving along a first Y-axis and a second Y-axis installedparallel to each other.

Also, it is preferred in the present invention that a pair of X-axes areinstalled to be capable of moving along a first Y-axis and a secondY-axis installed parallel to each other, and two head units are providedso that one can move along each of the X-axes, and two image sensors areprovided close to both sides of the conveyer.

To achieve the above objects, there is provided a method for mountingparts which is achieved by recognizing a particular part feeder where apart to be mounted is contained among a plurality of part feeders,moving a head unit to a position for picking up a part on the partfeeder, moving an image sensor installed to be capable of moving to aposition close to the particular part feeder, picking up a part from theparticular part feeder with a suction nozzle installed at the head unit,moving the head unit to a position above the image sensor, detecting animage of the part held by the suction nozzle, moving the suction nozzleto a printed circuit board from the image sensor, and aligning the partwith the printed circuit board while determining and compensating for anerror generated when the part is picked up, and mounting the alignedpart on the printed circuit board.

It is preferred in the present invention that the method for mountingparts further comprises a step of recognizing whether the image sensorhas moved to a position close to the particular part feeder after theimage sensor was supposed to have moved to the position close to theparticular part feeder.

Also, it is preferred in the present invention that the determining andcompensating is performed by determining the coordinates of the centerof the suction nozzle by detecting a position of a reference portionwhich is not covered by the part when the image is obtained, determiningthe coordinates of the center of the part from an image obtained by theimage sensor, calculating a value of correction of the part position bydetermining an offset of the part from the displacement of the center ofthe part held by the suction nozzle from the center of the suctionnozzle, and controlling a position for mounting the part with thesuction nozzle according to the value of correction.

According to another aspect of the present invention, there is provideda method for mounting a part which is achieved by calculating an optimalmovement path between a position for picking up a part from a partfeeder and a position for mounting the part on a printed circuit board,moving a head unit to the position for picking up a part from a partfeeder, calculating a position where a movement path of an image sensorcrosses a path formed between the part feeder and the position formounting the part along which the head unit moves, moving the imagesensor to the crossing position, picking up a part with a suction nozzleof the head unit, moving the head unit to a position above the imagesensor, detecting the part held by the suction nozzle by the imagesensor, moving the head unit to the position for mounting the part onthe printed circuit board, and aligning the part while determining andcompensating for an error generated when the part is picked up, andmounting the aligned part.

It is preferred in the present invention that the method furthercomprises a step of recognizing whether the image sensor has moved tothe cross position after the image sensor is moved to the crossposition.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail preferred embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a perspective view showing the structure of the typical partmounter;

FIG. 2 is a view schematically showing the path along which the headunit of FIG. 1 moves;

FIG. 3 is a view showing an image produced by an image sensing apparatusof a state in which a part is held by the suction nozzle;

FIG. 4A is a perspective view showing the structure of a part mounteraccording to the present invention;

FIG. 4B is a perspective view showing part of the part mounter shown inFIG. 4A;

FIG. 5 is a view schematically showing a method for mounting partsaccording to a first preferred embodiment of the present invention;

FIG. 6 is a flow chart for explaining the method for mounting partsaccording to the first preferred embodiment of the present invention;

FIG. 7 is a view schematically showing a method for mounting partsaccording to a second preferred embodiment of the present invention;

FIG. 8 is a flow chart for explaining the method for mounting partsaccording to the second preferred embodiment of the present invention;

FIGS. 9 and 10 are views showing states in which an error in holding apart is recognized on a monitor of the part mounter according to thepresent invention;

FIG. 11 is a flow chart for explaining a method of determining andcorrecting an error in holding a part according to the presentinvention; and

FIG. 12 is a plan view showing a part mounter of a double gantry type towhich the present invention is applied.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4A shows the structure of a part mounter for performing a methodfor mounting parts according to the present invention. Here, the samereference numerals as these appearing in FIG. 1 denote the same elementshaving the same functions. Referring to FIG. 4A, a part mounteraccording to the present invention includes the first and second Y-axes12 and 13 installed parallel to each other, the X-axis 11 installed tobe capable of moving along the first and second Y-axes 12 and 13, thehead unit 14 installed to be capable of moving along the X-axis 11, thesuction nozzle 15 installed at the head unit 14 to be capable ofrotating and moving up and down, and the conveyor 19 for transferringthe printed circuit board (PCB) 25 to positions where parts are mounted.The head unit 14 moves between the part feeders 18 a, 18 b, 18 c, 18 dand 18 e and the PCB 25. The suction nozzle 15 moves up and down androtates to hold parts and mount the held parts on the PCB 25.

According to one characteristic feature of the present invention, theimage sensor 46 for detecting a part held by the suction nozzle 15 ofthe head unit 14 is installed to be capable of moving. The image sensor46 is installed to be capable of moving while being close to aparticular part feeder for holding a part among the part feeders 18 a,18 b, 18 c, 18 d and 18 e of which one or more are provided. After thesuction nozzle 15 is lowered to hold a part, the head unit 14 moves justabove the image sensor 46, which is moved in advance near a particularpart feeder from which the part is picked up, and performs sensing.Thereafter, the part is mounted on the printed circuit board 25.

According to another characteristic feature of the present invention,the movement path of the image sensor 46 for detecting the part held bythe suction nozzle 15 of the head unit 14 may be set to cross linearpaths along which the head unit 14 moves to part mounting positions fromthe respective part feeders 18 a, 18 b, 18 c, 18 d and 18 e.

Furthermore, the head unit 14 moves along a substantially shortened pathbetween the part mounting positions and the respective part feeders 18a, 18 b, 18 c, 18 d and 18 e, and the image sensor 46 moves to theposition where the movement path of the image sensor 46 and the movementpath of the head unit 14 meet, so that the part held by the suctionnozzle 15 can be detected.

In FIG. 4A, a servo motor 33 and a ball screw 35 are applied to move theimage sensor 46. When the servo motor 33 rotates, the ball screw 35which is rotatably supported by a bearing 34 rotates. Since the ballscrew 35 is coupled to a bushing 32 installed at the image sensor 46,the image sensor 46 can move close to any of the part feeders 18 a, 18b, 18 c, 18 d and 18 e. As a controller (not shown) controls driving ofthe servo motor 33, while the suction nozzle 15 of the head unit 14picks up a part from one of the part feeders 18 a, 18 b, 18 c, 18 d and18 e, or before holding a part, the image sensor 46 moves in advance tothe meeting position close to the corresponding part feeder and waitsthere. In another example, a linear motor is used instead of the ballscrew 35.

FIG. 4B is a perspective view showing part of the head unit 14 providedat the apparatus of FIG. 4A. Referring to the drawing, at least one ofreference portions 132 a and 132 b is installed at one side of the headunit 14. The reference portions 132 a and 132 b are installed such that,when the image sensor 46 senses a part 135 held by the suction nozzle15, at least one reference portion can be viewed, that is, the referenceportions 132 a and 132 b are not covered by the part 135.

Providing the reference portions 132 a and 132 b is important in thatthe moving image sensor 46 (see FIG. 4A) recognizes an error generatedduring picking up a part. Since the position of the reference portions132 a and 132 b and the center of the nozzle 15 are values which areknown, when the image sensor 46 senses at least one of the referenceportions 132 a and 132 b, the position of the center of the suctionnozzle 15 can be determined from the position of the reference portions132 a and the 132 b and the relative positions of the center of thesuction nozzle 15 and the center of the part can be obtained. Thus, anerror during picking up a part can be recognized from these values. Amethod of recognizing an error during picking up a part will bedescribed later.

FIG. 5 is a view schematically showing a method for mounting partsaccording to a first preferred embodiment of the present invention. Thesame reference numerals as those in FIG. 4A denote the same elementshaving the same functions. Referring to the drawing, a part feeder is atray feeder, a stick feeder or a general feeder in which parts are woundaround a reel. Five part feeders 18 a, 18 b, 18 c, 18 d and 18 e areprovided like the preferred embodiment shown in the drawing. Also, theimage sensor 46 (see FIG. 4A) can move to a position close to each ofthe part feeders 18 a, 18 b, 18 c, 18 d and 18 e, as shown in thedrawing, and the positions of the image sensor 46 at that time areindicated by reference numerals 31 a, 31 b, 31 c, 31 d and 31 e. Whenthe ball screw 35 is driven by the servo motor 33 to rotate, the imagesensor 46 linearly reciprocates along a typical guide member (a linearmotion guide in the example shown in the drawing).

If the suction nozzle 15 picks up a part from the part feeder 18 b, forexample, and mounts the part at a position indicated by P2 on the PCB25, the image sensor 46 moves to the position indicated by referencenumeral 31 b so as to be positioned as close as it can get to the partfeeder 18 b. Thus, the movement path of the head unit 14 can be reducedto the shortest distance from the part feeder 18 b to the position 31 bof the image sensor 46. Also, the movement path of the head unit 14 fromthe position 31 b of the image sensor 46 to the position P2 for mountingthe part becomes the shortest distance. Likewise, when a part is pickedup from the part feeder 18 e and mounted on a position P5 on the PCB 25,the image sensor 46 moves to the position indicated by the referencenumeral 31 e. Next, the suction nozzle 15 of the head unit 14 holdingthe part moves to the position 31 e of the image sensor 46 so thatdetecting the part is performed. Then, the head unit 14 moves to theposition P5 for mounting the part along the shortest route. The aboveoperation applies in the same manner to the other positions P1, P2 andP3 and the other part feeders 18 a, 18 c and 18 d.

In an actual embodiment, a plurality of suction nozzles can be providedto a head unit. Accordingly, the head unit moves between a plurality ofpart feeders so that each suction nozzle can pick up a part, before thehead unit moves to the position directly above an image sensor. In thiscase, the image sensor moves close to a part feeder where the last partis picked up. As each suction nozzle of the head unit passes above theimage sensor, detecting is performed. Next, correcting positional errorsof the parts is performed according to information obtained from thedetecting of parts held by the respective suction nozzles of the headunit. Then the head unit moves above a PCB and the parts are mountedthereon.

FIG. 6 is a flow chart for explaining the method for mounting partswhich was described with reference to FIG. 5. Referring to FIG. 6, aparticular part feeder containing a part to be mounted, among aplurality of part feeders, is recognized prior to each performance ofmounting a part (step 51). Next, the head unit 14 is moved to theposition for picking up the part from the part feeder (step 52). Theimage sensor 46 is moved to the position close to the part feeder (step53). It is determined whether the image sensor 46 is at the correctposition (step 54). If it is determined that the image sensor 46 is notat the position close to the part feeder, the step of recognizing aparticular part feeder begins again. If it is determined that the imagesensor 46 is at the position close to the part feeder, the suctionnozzle 15 picks up a part from the particular part feeder (step 55). Thepart feeder holding the part moves just above the image sensor 46 (step56). Detecting an image of the part is performed (step 57). A signal forthe detected image of the part is used through data processing as datafor determining and correcting to an error in picking up the part andfor determining the position for mounting the part. The head unit 14 ismoved to the PCB 25 from the image sensor 46 (step 58). Whiledetermination of the part suction error is performed, the position formounting a part is determined and the part is mounted on the PCB 25(step 59).

FIG. 7 is a view showing a method for mounting parts according to asecond preferred embodiment of the present invention. The referencenumerals in the drawing which are the same as those in FIG. 4A denotethe same elements having the same functions. Referring to the drawing,part feeders are indicated by reference numerals 18 a, 18 b, 18 c, 18 dand 18 e. Also, an image sensor (not shown) can reciprocate along atypical guide member (not shown) when the ball screw 35 driven by theservo motor 33 rotates.

When a head unit (not shown) picks up a part from the part feeder 18 bto mount the part at the position indicated by reference numeral 61 b onthe PCB 25, a linear route connecting a position for picking up a parton the part feeder 18 b and a position 61 b for mounting the part on thePCB 25 is chosen as the movement path of the head unit. Here, since theimage sensor moves along the ball screw 35, the movement path of theimage sensor matches the lengthwise direction of the ball screw 35.While the head unit moves to the position 61 b for mounting a part onthe PCB 25 from the part feeder 18 b, the image sensor is positionedjust above the head unit at the time when the head unit and the imagesensor cross. Here, the position of the image sensor is indicated byreference numeral 31 b′ in FIG. 7.

Also, when parts are picked up from the other part feeders 18 a, 18 cand 18 d to be mounted at other positions 61 a, 61 c and 61 d on the PCB25, the image sensor is moved to a position where a line connecting therelevant part feeder and mounting position and the movement path of theimage sensor 31 cross. The positions are indicated by reference numerals31 a′, 31 c′, 31 d′ and 31 e′.

When the part held by the suction nozzle is sensed, a correction mayneed to be made considering an angle made by the image sensor 31 and thesuction nozzle. Such a case occurs in a part mounter using a multi-jointrobot, not in the gantry type part mounter shown in FIG. 4A. Forexample, when the head unit moves along a linear path to the partmounting position 61 a on the PCB 25 from the part feeder 18 a, and ifthe part is detected at the position 31′, an angle θ is formed between arectangular coordinate of the head unit and a rectangular coordinate ofthe image sensor. Thus, considering the above angle, calculation of theangle is needed in order to determine an error in picking up a part. Theangle θ can be automatically calculated by constructing a data base withrespect to the positions for mounting a part on the PCB, the position ofthe part feeder, and the current position of the image sensor on themovement path. Alternatively, as the suction nozzle holding a partpasses above the image sensor, image information is received so that anangle can be calculated.

To compensate for the calculated angle θ, the suction nozzle 15 isrotated or the image sensor 46 is rotated. For example, as the suctionnozzle 15 is rotated by the power from the servo motor (not shown), theangle θ is compensated for. In another example, the image sensor 46 isconfigured not only to reciprocate but also to rotate to compensate forthe angle θ.

FIG. 8 is a flow chart for explaining the method for mounting partsdescribed with reference to FIG. 7. Referring to FIG. 8, an optimalmovement path between a position for picking up a part from the partfeeder and a position for mounting a part on the PCB is calculated bythe controller of the part mounter (step 71). The head unit is moved tothe position for picking up a part on the PCB (step 72). The crossingpoint of the movement path of the image sensor and the movement path ofthe head unit is calculated (step 73). The image sensor is moved to thecrossing point (step 74). It is determined whether the image sensor ismoved to the crossing point (step 75). Here, if the image sensor is notprecisely moved to the crossing point, the crossing point isrecalculated and the step of moving the image sensor to the crossingpoint is repeated.

If the image sensor is positioned at the crossing point, the suctionnozzle of the head unit picks up a part (step 76) and the head unit ismoved just above the image sensor (step 77). The image of the pickedpart is detected (step 78). The detected image of the part is processedin a predetermined method so as to be used as information fordetermination of the part mounting position after an error in picking upa part is determined. Then, the head unit is moved to the part mountingposition on the PCB (step 79). The part is aligned and mounted at apredetermined position on the PCB with error correction (step 80).

In the case of a head unit having a plurality of suction nozzles, theimage sensor is positioned at the point where the movement path of theimage sensor and the shortest distance between the part picking positionof the part feeder where the last part is picked up by one of thesuction nozzles of the head unit and the part mounting position, cross.The head unit moves along the shortest linear path from the positionwhere the last part is picked up to the part mounting position. Whilethe head unit moves just above the image sensor positioned on the abovemovement path, information on position of the part is obtained bydetecting the image of the part. Each suction nozzle of the head unitrotates the part according to the position information obtained bydetecting while moving, and mounts the part on the PCB.

FIG. 9 shows the image of a part detected by the image sensor. Referringto the drawing, when the center of a monitor 97 is B, the center B ofthe monitor 97 matches the center of a suction nozzle 94 holding a part91. Elements indicated by reference numerals 92 and 93 on the monitor 97are the reference portions 132 a and 132 b of FIG. 4B detected anddisplayed on the monitor 97. Since the center of the suction nozzle 94of the part 91 can be determined by the reference portions 92 and 93,the displacement between the center of the suction nozzle 94 and thecenter O of the part 91 can be calculated.

That is, as shown in FIG. 4B, as at least one of the reference portions132 a and 132 b which are installed at the head unit 14 where thesuction nozzle 94 is installed is not covered by the part when the partis picked up, the displacement between the reference portions 132 a and132 b and the centers of the suction nozzle 15 can be determined. Thus,the position of the center of the suction nozzle 13 is obtained from theimage displayed on the monitor 97 by detecting the reference portions132 a and 132 b, so that the displacement of the center O of the partcan be easily obtained.

FIG. 10 shows another example of an image detected by the image sensorand displayed on the monitor. Referring to the drawing, when the centerof the monitor 97 is B, the center B of the monitor 97 and the center ofthe suction nozzle 94 holding a part 95 do not match. Even when thecenter B of the monitor 97 and the center of the suction nozzle 94 donot match, a positional error of the part 95 can be measured. In thiscase, even if the fixed coordinates of the image sensor are not set, anaccurate position for mounting a part can be obtained by calculating thecoordinates of the center of the part 95 and the value of a relativeposition of the suction nozzle 94.

That is, the center of the suction nozzle 94 holding the part 95 beingcovered by the part 95 is not shown on the monitor 97. However, theposition of the center of the suction nozzle 94 is obtained from thereference portions 92 and 93 displayed on the monitor 97 by detectingthe reference portions 132 a and 132 b in FIG. 4B. The position of thecenter of the part is calculated from the detected image and thedisplacement between the two centers is obtained. The displacement canbe treated in rectangular coordinates or in angular coordinates.

FIG. 11 is a flow chart for explaining a method of determining an errorgenerated while picking up a part, by the image sensor described withreference to FIGS. 9 and 10. Referring to FIG. 11, the part held by thesuction nozzle 94 is moved, passing just above the image sensor, and theimage of the part is detected (step 210). To detect the amount ofdeviation of the parts 91 and 95 from the center of the suction nozzle94, the position of the center of the suction nozzle 94 is calculated byusing the position of the reference portions 92 and 93 which are notcovered by the parts 91 and 95, and a value of a relative position isobtained (step 220). The center of each of the parts 91 and 95 isobtained from the image of the part (step 230). An offset value of thepart is obtained by comparing the value of the relative position and thevalue of the position of the center of the part, and a value of theerror in the position of the part is obtained (step 240). Finally, asthe controller is operated according to the error correction value,controlling the suction nozzle 94 to align the parts 91 and 95 isperformed (step 250). Then, the parts are mounted.

Obtaining the relative position of the nozzle with at least onereference portion as above is possible because the head unit itself doesnot rotate in a gantry type part mounter and the relative positioninitially set between the reference portion of the head unit and thecenter of the suction nozzle is not changed. Thus, the value can becalculated with at least one reference portion. However, when themeasurement is performed with two reference portions, even if a changeoccurs to a relative angle between axes for moving the head unit in Xand Y directions in a gantry type part mounter, the center of thecurrently held part and the relative position of the suction nozzle canbe calculated. Also, even when the head unit itself rotates, the valuecan be calculated.

FIG. 12 is a plan view showing a part mounter of a double gantry type towhich the present invention is applied. Referring to the drawing, afirst X-axis 310 and a second X-axis 320 are movably installed on afirst Y-axis 330 and a second Y-axis 340. A first head unit 380 isinstalled on the first X-axis 310 to be capable of moving along thefirst X-axis 310. A second head unit 390 is installed on the secondX-axis 320 to be capable of moving along the second X-axis 320. A PCB400 is moved by a conveyor 370 and part feeders 410 and 420 for therespective head units are installed close to both sides of the conveyor370.

In a double gantry type part mounter as shown in FIG. 12, two imagesensors are installed. That is, as shown in the drawing, a first imagesensor 350 and a second image sensor 360 are installed close to bothsides of the conveyor 370. When each of the head units 380 and 390 picksup a part from the part feeders 410 and 420, each of the image sensors350 and 360 moves close to each of the part feeders 410 and 420 todetect an image of the picked up part. Thus, the speed of mounting partsincreases.

As described above, in the part mounter and the method for mountingparts according to the present invention, since the image sensor movesclose to a particular part feeder or crosses the movement path of thepart picking portion, the movement path of the part picking portion isshortened and thus the speed of mounting a part increases and theefficiency of mounting is improved. Also, an error generated duringpicking up a part can be easily determined and corrected with the movingimage sensor.

It is noted that the present invention is not limited to the preferredembodiments described above, and it is apparent that variations andmodifications by those skilled in the art can be effected within thespirit and scope of the present invention defined in the appendedclaims.

1. A method for mounting parts comprising the steps of: recognizing aparticular part feeder where a part to be mounted is contained among aplurality of part feeders; moving a head unit to a position for pickingup a part on the part feeder; moving an image sensor installed to becapable of moving to a position close to the particular part feeder;picking up a part from the particular part feeder with a suction nozzleinstalled at the head unit; moving the head unit to a position above theimage sensor; detecting an image of the part held by the suction nozzle;moving the suction nozzle to a printed circuit board from the imagesensor; and aligning the part with the printed circuit board whiledetermining and compensating for an error generated when the part ispicked up, and mounting the aligned part on the printed circuit board,wherein the determining and compensating is performed by the steps of:determining the coordinates of the center of the suction nozzle bydetecting a position of a reference portion which is not covered by thepart when the image is obtained; determining the coordinates of thecenter of the part from an image obtained by the image sensor;calculating a value of correction of the part position by determining anoffset of the part from the displacement of the center of the part heldby the suction nozzle from the center of the suction nozzle; andcontrolling a position for mounting the part with the suction nozzleaccording to the value of the correction.